Actor Aaron Eckhart, appearing on the cover of the upcoming issue Muscle & Fitness, opens up about the monstrous training regimen he underwent for his role in the highly-anticipated film I, Frankenstein.

“I wanted to be strong like a gorilla — to have that animal instinct,” the A-lister told Muscle & Fitness of the unrelenting six-month training plan, in which he worked out six days a week. “When you’re pushing yourself that far, your intellect takes a back seat and that animal aspect takes over.”